Possible Isotopic Evidences of Post Marinoan of Neoproterozoic III in Three Gorges Area, China
Abstract
Well world widely correlated Neoproterozoic III, upward includes Doushantuo Formation and Dengying Formation, overlays tillite of Nantou Formation and Gucheng Formation in Three Gorges area, China. The section has well controlled on biostratigraphy and sedimentology, such as complex of small shelly fossils yield around Precambrian-Cambrian boundary at the top of the section, Vendotaenids yield in the lower part of Dengying Formation, acritarches in Doushantuo Formation, and cap dolomite at the base of Doushantuo Formation which overlay tillite unit of Nantou Formation at the base of the section. Strontium, carbon oxygen isotope presents significant excursions in this well-developed carbonate section that is located at Wuhe near Zhigui in the area. 1) Carbon isotope (δ13C) dramatic dropped from 4‰ to "C8‰ (PDB in this paper) near the boundary of Doushantuo and Dengying Formation, and elevates around 4‰ at lower part of Dengying Formation where oxygen isotope (δ18O) raises to 0.5‰ from "C7‰ at the upper part of Doushantuo Formation. Strontium isotopic ratio (87Sr/86Sr in this paper) is discovered a peak as high as 0.7100 in the base of Dengying Formation, and exhibits important excursions across the boundary from 0.7077 on the upper part of Doushantuo Formation and 0.7084 on the lower part of Dengying Formation. 2) A world widely typical excursion of carbon and strontium isotopes are confirmed span the boundary of Precambrian-Cambrian where controlled by a complex of small shelly fossils at the top of the section. 3) Abnormally isotopic excursions around the boundary of Doushantuo and Dengying Formation may be the possible evidence of post Marinoan ice age.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2002
- Bibcode:
- 2002AGUFMPP12B..06W
- Keywords:
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- 1040 Isotopic composition/chemistry;
- 1827 Glaciology (1863);
- 4806 Carbon cycling;
- 4870 Stable isotopes;
- 9619 Precambrian